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Author Topic: Fostex FR2-LE (Oade) / Audacity Clipping Question  (Read 567 times)

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Offline EvilEye

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Fostex FR2-LE (Oade) / Audacity Clipping Question
« on: December 02, 2016, 11:35:38 AM »
OK, recorded Tedeschi Trucks last night, 9th row dead center at the Boston Orpheum, AKG ck61 Actives -> Fostex FR2-LE Oade Mod.

I've ran the FR2LE for a number of years, am very comfortable and familiar with it, including using in the field, in the dark, etc.  It has the following meters:

1.  An 8 segment LCD peak meter, with the seventh segment being 0dB and the last segment being "OL" (Overload").
2.  Two Red LEDs on the side, directly above two mic trim pots to indicate clipping on the mic preamps,   
3.  6 Colored LEDs on the side for each channell (12 in all) Two Green, Three Orange, One Red. 
     The Oranges are -12, -6, -3, and Red is "OL" - Overload".

I ran it a little hot as I usually do, set to peak near / just below 0dB on the top meter, the side lights were visible to me throughout the show, and I kept my eye on them, the Mic Preamp Clip lights never came on, Trim Pots were at 12.  The Level Meter LEDs were either-6 or -3, never OL, never saw a red light all night, when I play back the recording on the FR2LE, no red lights, the top LCD Meter never hits OL.

BUT.....

1.  When I import it into Audacity, it looks slightly over. 
2.  When I select "Show Clips" it shows the Clips in Red, lots of them (See attached pic).
3.  If I use Amplify or Normalize to get to 0dB, it shows a 0dB adjustment,
4.  If I use Amplify to push it down to -1.0dB, it shows an adjustment of -1.0dB.

It's hard to tell if there's any minor distortion, because at those points Audacity shows red, the band is thundering, Derek is wailing, of course he's playing through an overdriven tube amp (on purpose).  It's certainly not crackling / brickwalling, anything like that.

What gives?

I'd tend to trust the Fostex with the Oade re-built input stage rather than Audacity.

I'm recording them again Saturday 8th row on the right side of the center section, I'll run a little more conservatively then.

Oh & BTW, head of security told me about 4 times I had to keep the mics at "Shoulder Height" per direct request from the band management.  Thankfully it wasn't like an ABB show with a bunch of drunken people making lots of noise, really no problems with talkers or clapping or anything.

The band had two pairs of audience mics on either side of the stage - an LD and a SD, and at least one XY Coincident pair at the soundboard (why they're running XY, IDK....)

TIA.
 
 
AKG 460/ck61/ck63 /ck2 / ck8
AT853RX  - O/SC/C/H
Nbob AKG actives / Naiant PFAs / Bumblebee MiAGi-II Silver Cables
FR2-LE (Oade mod) / PCM-M10 / DR-70D
SD MP-2 / CA-9100

Offline mjwin

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Re: Fostex FR2-LE (Oade) / Audacity Clipping Question
« Reply #1 on: December 02, 2016, 12:22:52 PM »
The red highlight is a useful (if sometimes scary) feature of Audacity, but sadly it's telling the truth. To me, your recording looks a bit hot for comfort anyway.  I wouldn't blame the input pres or the Oade mod, it's just digital overload.

An annoying quirk of the FR2LE is that the LED display seems to operate in the analog domain and doesn't trap instantaneous peaks which hit the digital endstop!    I tend to record at fairly conservative levels, and have only had this problem (ie clipping going unnoticed until I open up the file to edit) with applause, or sudden peaks on environmental recordings which will get edited out anyway. 

The acid test is always whether it sounds ok. Generally, if it's only a couple of samples which are over in each peak amidst a loud recording, it's pretty inaudible anyway.  If you zoom in to the peaks, does the waveform look truncated?

With digital recording 0dB is a brick wall, and coming from analog tape it took me a while to back off a bit. Now, when recording live sound & monitoring the display, I  usually aim for -12dB peaks and treat -6dB as "over" just in case!  The low noise pres on the FR2LE allow for plenty of margin here with no probs. 

Offline dallman

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Re: Fostex FR2-LE (Oade) / Audacity Clipping Question
« Reply #2 on: December 02, 2016, 12:33:58 PM »
It is virtually impossible to know why this outing was different, you are not using an external preamp, so why the wave file is apparently larger than your meters indicated and you know those meters well, would only be speculation. I'd say if it sounds ok to your ears, that is what really matters and perhaps you barely dodged the bullet.

You do not say if you recorded at 16 bit or 24 bit. I see you were at 44.1kHz, but do not see a bit rate. If you want to keep you files clean, I'd recommend the following:

Record at 24 bit, which allows you more freedom to edit without reducing the quality of your digital recording. I like 24/48 for may reason not worth mentioning here, but 24/44.1 is ok if that is what you prefer. At 24 bit, there is no reason to run hot. Running hot at best will sound slightly more compressed to most ears, and you run the risk of overload (as you have stated above) which as you know really cannot be fixed. At 24 bit you can run more conservatively and then boost in audacity to a higher level, and it will likely sound a little better too, less compressed. Unlike the old analog days, when we ran hot to minimize take hiss, running lower is better as you can boost with no hiss at all, no degradation to your recording.

When done, you can dither your finished file back to 16/44.1 easily. I do not know audacity well as I use soundforge, but there is always R8 Brain, a free program to dither back.
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Offline EvilEye

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Re: Fostex FR2-LE (Oade) / Audacity Clipping Question
« Reply #3 on: December 02, 2016, 01:35:04 PM »
thanks guys.  zooming in on the samples, it's pretty well peppered.

listening to it, though, sounds great to me, I probably wouldn't even have thought it clipped if I didn't see the waveforms.

I always run 24 Bit, either 88khz (on the probably erroneous theory that the math is easier to get to 44.1) or this one I did at 96khz.

I somehow thought running proper levels, rather than running low and amplifying in post, would result in a better S/N ratio.  I guess not.

I go back to the days of running cassettes, so always try to run the levels to peak.
AKG 460/ck61/ck63 /ck2 / ck8
AT853RX  - O/SC/C/H
Nbob AKG actives / Naiant PFAs / Bumblebee MiAGi-II Silver Cables
FR2-LE (Oade mod) / PCM-M10 / DR-70D
SD MP-2 / CA-9100

 

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